1. Field of the Invention
The present invention relates to a fluid fuel obtained from coal in the form of a liquid slurry of particulate carbon and relates to a process for preparing such fluid fuel.
2. Description of the Prior Art
Coal is a combustible natural substance containing carbon and hydrocarbons which are low in hydrogen content. The transportation, storage and use of coal as a fuel presents problems because of (a) the solid nature of the product; (b) the non-uniformity of the chemical and physical composition; (c) the omnipresent ash content which must be discarded following combustion of the coal; (d) the presence of sulfur in coal which appears in the coal combustion gases as sulfur oxides which present atmospheric pollution problems.
The technical literature exhaustedly proposes conversion of coal into liquid or gaseous fuels which avoid the recited problems of coal utilization. Overwhelmingly the objective of coal conversion heretofore has been to produce hydrocarbonaceous fuels such as gases (methane, water gas, producer gas and coal distillation gases) or liquid fuels by various combinations of solvent extraction of coal; coal distillation; hydrogenation; reformation (e.g., Fisher-tropsch, et cetera).
Overwhelmingly the coal utilization technology has recognized coal to be a high carbon, low hydrogen content fuel and has attempted to recover the hydrogen-rich ingredients for further upgrading into hydrogen-rich liquid or gaseous fuels and to burn or react the surplus carbon content to provide thermal energy for the remainder of the process and to generate hydrogen-rich gas to offset the hydrogen-deficiency of the coal.
The ODELL patent (U.S. Pat. No. 1,964,744) describes a process for producing carbon black by obtaining carbon monoxide (possibly from coal) and converting the carbon monoxide through the reverse Boudouard reaction: EQU 2CO.fwdarw.CO.sub.2 +C
ODELL recovers carbon black as a high purity specialty product. The ODELL process is understandably profligate in energy consumption, understandably, in view of the relatively low value of energy at the time the ODELL process was proposed (1930). ODELL recognizes the importance of recovering carbon dioxide from the Boudouard reaction and recirculating the carbon dioxide through a carbonaceous fuel bed to create additional carbon monoxide. ODELL further recognizes that elevated pressures promote carbon production in the Boudouard reaction and recognizes that steam can be employed as a moderating gas to regulate the Boudouard reaction exotherm.
As far as can be determined, in more than 50 years since the ODELL patent, there have been no commercial attempts to produce carbon black via the ODELL process.
There have been prior suggestions that coal be converted primarily to carbon and that the resulting high purity carbon be admixed with water to produce an aqueous slurry which functions as a pumpable fuel of essentially zero ash content and essentially zero sulfur content for use in furnaces, internal combustion engines, turbines and the like. Such suggestions have proposed hydrogenating coal to maximize methane production and to convert the methane by thermal decomposition into hydrogen gas which is recycled in the process and high purity carbon for subsequent combination with water to form an aqueous slurry constituting a fluid fuel.